1. Field of the Invention
This invention relates to an electrical device for vaporizing volatile substances such as insecticide from solid carriers comprising a vertically disposed electrical heating plate in a housing and a tablet feed passage extending substantially horizontally past the heating surface of the heating plate with a tablet insertion slot in the side of the housing and further comprising contact pins for insertion into a power socket or the like on the back of the housing.
2. Statement of the Related Art
An electrical vaporizer of this type is described in U.S. Pat. No. 4,214,146 and corresponding published German patent application No. 27 30 855. In the associated oblate ellipsoid shaped housing, a disc shaped heating element and an insecticide tablet are arranged vertically one on top of the other. The tablet is disposed immediately behind a grating which is permeable to the vaporized insecticide and which forms part of the front of the housing, extending substantially vertically in use. The tablet is brought into the operational position through a slot in the side of the housing through a horizontal feed passage. The feed passage may extend transversely through the housing. The insecticide is vaporized almost exclusively by diffusion through the open grating in the front of the housing; ventilation slots provided in the back of the housing are virtually inaccessible to the vapors coming from the tablet. One disadvantage of this known vaporizer is that the vaporized substance cannot normally be dispersed in the surrounding atmosphere by convection, but only by molecular movements, because of the concentration gradient maintained by the vaporization. The condensation of the vaporized substance from the corresponding outlet openings is particularly troublesome. Furthermore, a fan may have to be used for dispersing or rather circulating the vaporized substance.
Another vaporizer for an insecticide, designed to be plugged into an electrical wall socket, is described in published British patent application No. 2,003,034 and corresponding published German patent application No. 28 25 674. The associated housing comprises a lower chamber with air inlet openings and an upper chamber with air outlet openings. Arranged at the boundary between the lower and upper chambers are an electrical heater and, vertically thereover on a grid of pins or teeth, a tablet of insecticide. The tablet, the grid supporting it and the heating element are designed and arranged in such a way that, in addition to its actual function (i.e. vaporization of the insecticide), the heating element is able by convection to generate an air stream flowing vertically through the air inlet openings into the housing, around the insecticide tablet in the housing and then back out of the housing through the air outlet openings. In this vaporizer, the resistance heater by which the insecticide tablet is vaporized has to be heated far beyond the temperature necessary for vaporizing the insecticide, because there is no direct contact between the tablet and the heating element. accordingly, a large proportion of the heating energy is lost without being used and high heating temperatures are necessary to evaporate from the particular tablet substances that are difficult to vaporize. Another disadvantage of the known vaporizer is the on/off indicator lamp because it deflects the convective air flow and hence interferes with permeation of the insecticide.